1. Field of the Invention
The present invention relates to a motor-driven device for preadjusted frequency tunings for a klystron. This device makes use of a known mechanical base of pistons which are inserted to a greater or lesser extent in the resonant cavities of a klystron, these pistons being extended by rods thrust by springs against adjusting screws supported by a carriage. The distinctive feature of the device lies in the fact that it does not adopt the same locking position at the different frequencies for the plate on which the springs are applied for maintaining the rods of each piston in contact with the adjusting screws. This makes it possible to employ shorter springs which are less bulky and work at their optimum value of compression. Moreover, electric switches integrated in the mechanical assembly control the respective positions of the moving parts and ensure positioning of the plate and operational safety of the system.
2. Description of the Prior Art
Klystrons are microwave generators provided with cavities. In order to obtain high power, it is known to associate a plurality of resonant cavities. One movable wall of each cavity is constituted by a piston, the displacement of which makes it possible to vary the volume of the cavity and consequently the frequency of the klystron.
The instantaneous passband of a klystron is much smaller than the mechanical tuning range, namely the frequency domain in which it can be operated. For example, in the case of a klystron which operates between 5.9 and 6.4 GHz, its tuning range of 500 MHz can be divided into twelve channels including the passband and 45 MHz in each case. In order to displace the passband within a tuning range or in other words in order to change from one channel to another, it is necessary to change the resonant frequencies of the different cavities. One method commonly employed consists in displacing a piston within resonant cavities having rectangular cross-sections. Said piston ensures an electrical contact with the sides and behaves as a movable wall of the cavity. Vacuum-tightness is ensured by means of a deformable metallic bellows seal placed behind the piston and welded to the edges of the cavity and to the rod which forms an extension of the piston.
A different position of each piston corresponds to each passband or channel. The pistons are rigidly fixed to a rod which can be displaced by means of a screw-thread. At each change of channel, it is accordingly necessary to carry out a number of adjustments corresponding to the number of pistons and therefore of cavities. It is this method which is usually employed for large klystron tubes.
For this reason, mechanical memorization devices have been designed. During operation, the piston rods are applied against movable stops. These stops are screws which are inserted to a greater or lesser extent in a movable carriage which is rectangular or in the form of a revolver with a wheel pivoted about its axis. A set of screws positioned in front of the piston rods corresponds to each channel. It is therefore necessary to have a number of screws equal to the product of the number of channels times the number of cavities.
It is also known to equip this mechanical memorization device with electric motors which replace any human agency for changing the frequency but these motors are controlled by a wired logic which is independent of the memorization device. The plate on which the springs are applied is always restored to the same locking position.
This motor-drive system has two drawbacks. The springs, one end of which is always in the same locking position, must have a sufficient length to exert a suitable pressure force in the two extreme cases of the longest adjusting screws corresponding to high frequencies and of the shortest adjusting screws corresponding to low frequencies. The springs are therefore bulky. Furthermore, the motors are programmed without knowing the mechanical state of the memorization device since this latter is purely mechanical and does not have any sensor. Thus, if an incident occurs such as pistons which have seized, screw-holding carriage in an intermediate position, and so on, the action of the electric motors may cause damage to at least the mechanical memorization device and in some instances to the klystron cavity as well.
The device in accordance with the invention makes it possible to overcome this disadvantage by intelligent control of the motors. Electric contactors integrated in the device control the position of the mechanical moving parts and control the operation of the motors. Furthermore, two contactors check the position of the two ends of each spring. Thus they stop the locking motor as soon as all the springs have attained a length which corresponds to an optimum compression ratio. This means that the springs are short and that the plate on which the springs are applied is arrested in a locking position corresponding to each frequency. Thus the displacement of the plate compensates for the lack of deflection of short springs.